1. Field of the Invention
The present invention relates to an active device array substrate and method for repairing the same, and more particularly to a thin film transistor array substrate and method for repairing the same.
2. Description of the Related Art
A thin film transistor liquid crystal display (TFT LCD) is mainly composed of a thin film transistor array substrate, a color filter array substrate and a liquid crystal layer. Wherein, the thin film transistor array substrate is composed of plural thin film transistors arranged in array and pixel electrodes corresponding to the thin film transistors. The thin film transistors serve as the switch devices of pixel units. In order to control each pixel unit, scan lines and data lines coupled to the thin film transistors are used to select the pixel unit. By applying appropriate operating voltages, data corresponding to the pixel unit is displayed.
The development of LCD is in the trend for requirements of high brightness, high contrast, large screen size and wide view angle. In order to improve the view angle of LCD, several wide view angle techniques have been proposed. The common types of wide view angle LCDs at present are, for example, Multi-Domain Vertical Alignment (MVA) LCD, In-Plane Switching (IPS) LCD, and Fringe Field Switching (FFS) LCD. For MVA LCD, plural slits are formed on a pixel electrode. Plural strip protrusions are disposed over a corresponding color filer array substrate. By incorporation of the slits and protrusions, liquid crystal molecules in the liquid crystal layer will tilt to different directions to achieve the purpose of wide view angle display effect.
Note that in the prior art technology, in order to improve functions of storing and maintaining display data by a pixel unit, a portion of the pixel electrode is generally used to cover over the scan line or the common line to form a storage capacitor (Cst) with a metal-insulator-ITO (MII) structure. In addition, when forming the data line, the source region and the drain region, a upper electrode further is disposed between the pixel electrode and the corresponding common line or scan line. The pixel electrode electrically connects with the upper electrode so that the upper electrode, the common line or the scan line, and a dielectric layer formed between them forms a storage capacitor with a metal-insulator-metal (MIM) structure.
FIG. 1A is a top view of a portion of a prior art thin film transistor array substrate with a MIM storage capacitor. FIG. 1B is a cross sectional view of the structure of FIG. 1A taken along A-A′. Referring to FIGS. 1A and 1B, a portion of a pixel electrode 150 is over a corresponding common line 110. A upper electrode 130 is disposed between the pixel electrode 150 and the corresponding common line 110. In addition, a dielectric layer 120 is disposed between the upper electrode 130 and the corresponding common line 110 to electrically isolate the upper electrode 130 from the corresponding common line 110. Another dielectric layer 140 is disposed between the upper electrode 130 and the corresponding pixel electrode 150. Wherein, the dielectric layer 140 comprises a contact hole 142 so that the upper electrode 130 electrically connects with the pixel electrode 150 through the contact hole 142. Accordingly, the common line 110, the dielectric layer 120 and the upper electrode 130 constitute a MIM storage capacitor 102.
However, the conventional process of fabricating the thin film transistor array substrate may cause the storage capacitor defective due to process defect or other reasons. FIGS. 2A-4A are top views showing various prior art defective MIM storage capacitors. FIGS. 2B-4B are cross sectional views of the structures of FIGS. 2A-4A taken along A-A′.
Referring to FIGS. 2A and 2B, a defect 122 exists in the dielectric layer 120 between the common line 110 and the upper electrode 130. The defect 122 may be a particle or a hole resulted from process contamination, for example. Charge leakage between the upper electrode 130 and the common line 110 will occur because of the defect 122. In FIG. 3A (please redrew 170 for enhancing material residue) and 3B, in the prior art method of fabricating a data line 160 and the upper electrode 130, a conductive material 170 such as aluminum, may be remained between the data line 160 and the upper electrode 130, and the pixel electrode 150 may be electrically shorted to the data line 160 via the upper electrode 130.
In FIGS. 4A and 4B, in the prior art method of fabricating the pixel electrode 150, a conductive material 180 such as indium-tin-oxide (ITO) may be remained between two neighboring pixel electrodes that the adjacent pixel electrodes 150 are electrically shorted to each other. Regardless which situation described above occurs, the pixel unit will not normally display and as a result the displaying quality of the LCD becomes worse.